Abstract
Metastable face-centered cubic (fcc) Co was grown epitaxially on (111) Si with an intermediate Cu layer in an ultrahigh vacuum chamber at room temperature. The metastable fcc-Co was grown to extend to a thickness of 30 nm. Polycrystalline and epitaxial hexagonal close-packed (hcp) Co were grown on (111) Si without and with 3 nm or thicker intermediate Cu layer, respectively. The key to the successful growth of fcc-Co is to deposit Co directly onto a thin (2 nm or thinner) interface compound ζ-Cu, which is of hcp structure and consisting of 11.2 to 14.0 at.% Si. The growth of the metastable phase is attributed to the attainment of an appropriate electron/atom ratio at the interface to favor the formation of the fcc-Co.